Revert of "Remove non-versioned elections (2602)" pull request
Merge pull request #3114 from lutovich/2.1-rolling-upgrade-from-2.0

[2.1] Revert of "Remove non-versioned elections (2602)" pull request
Merge remote-tracking branch 'upstream/2.1-maint'

Conflicts:
	enterprise/ha/src/test/java/org/neo4j/ha/upgrade/RollingUpgradeIT.java
Merge pull request #3132 from davidegrohmann/merge-2.1-into-master

Merge 2.1 into master